October 3, 2012

Scientists at the University of Minnesota have invented a unique microscale optical device that could dramatically increase download speeds while lowering bandwidth costs.

The device uses the force generated by light to rapidly turn a mechanical switch of light on and off, a breakthrough that offers advances in computation and signal processing using light instead of electrical current — offering greater performance and lower power consumption.

“This device is similar to electromechanical relays but operates completely with light,” said Mo Li, an assistant professor of electrical and computer engineering in the University of Minnesota´s College of Science and Engineering.

The work is based on a previous discovery by Li and colleagues in 2008, which found that nanoscale light conduits can be used to generate a strong enough optical force to mechanically move an optical waveguide.

With the current device, the researchers discovered that this force of light is so strong that the mechanical property can be dominated completely by the optical effect, rather than its own mechanical structure.

The researchers amplified this effect to control additional colored light signals at a much higher power level.

“This is the first time that this novel optomechanical effect is used to amplify optical signals without converting them into electrical ones,” Li said.

Glass optical fibers carry many communication channels using unique wavelengths assigned to each channel. In optical cables, these channels do not interfere with each other, a characteristic that ensures the efficiency of a single optical fiber to transmit more information over very long distances.

But this benefit also has a cost, in that optical devices could not allow the various channels of information to control each other easily. Li´s discovery overcomes this limitation.

The new device has two optical waveguides, each carrying an optical signal. Placed between the waveguides is an optical resonator in the shape of a microscale donut, similar to a mini-Hadron collider. Inside the optical resonator, light can circulate hundreds of times, gaining intensity.

Using this resonance effect, the optical signal in the first waveguide is dramatically boosted in the resonator, generating a strong optical force on the second waveguide. The second waveguide is released from the supporting material so that it moves in oscillation, like a tuning fork, when the force is applied on it.

This mechanical motion of the waveguide changes the transmission of the optical signal. Because the power of the second optical signal can be many times greater than the control signal, the device serves as a mechanical relay to amplify the input signal.

Li´s device can currently operate at one million times per second, but the researchers expect to improve this to several billion times per second.

The mechanical motion of the optical device is already fast enough to connect radio-frequency devices directly with fiber optics for broadband communication.

The research was published Tuesday in the journal Nature Communications, and can be viewed here.

Image 2 (below): University of Minnesota researchers have invented a novel microscale mechanical switch of light on a silicon chip.